Damping thermoplastic elastomer articles with low compression set

ABSTRACT

An article is formed from a thermoplastic elastomer compound that includes styrenic block copolymer and high softening point tackifier. The styrenic block copolymer has a Copolymer Tan Delta Peak Temperature and the thermoplastic elastomer compound has a Compound Tan Delta Peak Temperature. The Compound Tan Delta Peak Temperature is greater than the Copolymer Tan Delta Peak Temperature. The article exhibits useful damping properties at or above room temperature while also exhibiting low compression set, which makes the article especially suitable for use as a seal or a gasket.

CLAIM OF PRIORITY

This application claims the benefit of U.S. Provisional Patent Application Ser. Nos. 62/114,719 filed on Feb. 11, 2015, and 62/114,701 filed on Feb. 11, 2015, each of which is hereby incorporated by reference in its entirety.

FIELD OF THE INVENTION

This invention relates to thermoplastic elastomer compounds and articles formed therefrom which exhibit useful damping properties at or above room temperature while also exhibiting low compression set properties.

BACKGROUND OF THE INVENTION

Demand exists in a variety of applications for materials that exhibit damping properties. In general, damping is the dissipation of mechanical energy from a system. Damping can be important in applications such as electronics, sound isolation, automotive and transportation, building and construction, household appliances, industrial equipment, firearms, healthcare and medical devices, and personal and/or sports protection.

The capacity of a material for damping is related to its peak temperature of the tangent of delta (Tan Delta Peak Temperature), which can be determined by dynamic mechanical analysis (DMA) as described, for example, by M. P. Sepe in “Thermal Analysis of Polymers”, Rapra Review Reports, Vol. 8, No. 11, 1997, which is incorporated herein by reference. The tangent of delta (Tan Delta) of a material is the ratio of its loss modulus (E″) to its storage modulus (E′). Consequently, as the value of Tan Delta increases, the response of the material is relatively more viscous than it is elastic, which thus provides greater damping. When graphically depicted against temperature, a Tan Delta curve includes a prominent peak at a particular temperature, which is the Tan Delta Peak Temperature and also can be representative of or comparable to the glass transition temperature (Tg) of the material. In general, a material with a Tan Delta Peak Temperature which is relatively nearer to an application temperature, such as at or above room temperature, will possess better damping properties than a material with a Tan Delta Peak Temperature which is relatively lower than the application temperature.

Demand also exists in a variety of applications for materials that exhibit low compression set. In general, compression set is the permanent deformation of a viscoelastic material after being subjected to a constant stress and an elevated temperature. Low compression set is desirable, for example, in sealing and gasket applications in various industries. Disadvantageously, however, conventional low compression set seals and gaskets made from crosslinked EPDM or silicone rubbers do not exhibit good damping together with low compression set.

Thermoplastic elastomers (TPEs), which are polymer materials that exhibit elasticity while remaining thermoplastic, can be used for damping applications and also can be used for low compression set applications. Thermoplastic elastomers can include styrenic block copolymers (SBC), thermoplastic vulcanizates (TPV), thermoplastic olefins (TPO), copolyesters (COPE), thermoplastic urethanes (TPU), copolyamides (COPA), and olefin block copolymers (OBC).

Some commercially available SBCs, such as HYBRAR 5127 available from Kuraray Co., Ltd., are known to exhibit vibration damping properties at room temperature. HYBRAR 5127 has a Tan Delta Peak Temperature that is reported to be 20° C. (i.e., about room temperature). HYBRAR 5127 can be formulated into conventional TPE compounds that exhibit effective room temperature damping, but typically only if the TPE compounds contain at least 40 weight percent of HYBRAR 5127. Using such a high level is economically disadvantageous because HYBRAR 5127 is a relatively expensive ingredient. Additionally, TPE compounds including HYBRAR 5127, which is a non-hydrogenated and relatively low molecular weight material, typically exhibit relatively poor UV/weathering stability, insufficient high temperature durability, and high (i.e., poor) compression set, which makes such TPE compounds unsuitable for applications that require good damping and low compression set, such as sealing and gasket applications.

SUMMARY OF THE INVENTION

Consequently, a need exists for TPE compounds and articles formed therefrom which are relatively low cost and exhibit useful damping properties at or above room temperature while also exhibiting low compression set properties.

The aforementioned needs are met by one or more aspects of the present invention.

It has been found that, by adding high softening point tackifier to styrenic block copolymer to provide a thermoplastic elastomer compound, the Copolymer Tan Delta Peak Temperature of the styrenic block copolymer can be shifted to a higher temperature (i.e., the Compound Tan Delta Peak Temperature) and, thereby, the damping capacity of the styrenic block copolymer can be increased for an intended end-use application at a given temperature, such as at or above room temperature. Surprisingly, such thermoplastic elastomer compounds and articles formed therefrom not only exhibit useful damping properties at or above room temperature, but also have useful low compression set properties.

One aspect of the invention is a thermoplastic elastomer compound that includes styrenic block copolymer and high softening point tackifier. The styrenic block copolymer has a Copolymer Tan Delta Peak Temperature and the compound has a Compound Tan Delta Peak Temperature. The Compound Tan Delta Peak Temperature is greater than the Copolymer Tan Delta Peak Temperature.

Another aspect of the invention is an article formed from the aforementioned thermoplastic elastomer compound. The article has a compression set of less than about 50%, or less than about 40%, or less than about 30%, at 70° C. for 22 hours according to ASTM D395.

A further aspect of the invention is a multi-component plastic article including at least two components formed from different thermoplastic materials and in which at least one of the different thermoplastic materials is the aforementioned thermoplastic elastomer compound.

An even further aspect of the invention is a method of making an article, such as a gasket or a seal, which has damping properties at or above room temperature and low compression set. The method includes the step of shaping the article from the aforementioned thermoplastic elastomer compound.

Features of the invention will become apparent with reference to the following embodiments. There exist various refinements of the features noted in relation to the above-mentioned aspects of the present invention. Additional features may also be incorporated in the above-mentioned aspects of the present invention. These refinements and additional features may exist individually or in any combination. For instance, various features discussed below in relation to any of the described aspects of the present invention may be incorporated into any of the described aspects of the present invention alone or in any combination.

EMBODIMENTS OF THE INVENTION

In some embodiments, the present invention is directed to a thermoplastic elastomer compound that includes styrenic block copolymer and high softening point tackifier. In other embodiments, the present invention is directed to an article formed from the aforementioned thermoplastic elastomer compound. In further embodiments, the present invention is directed to multi-component a plastic article in which at least one thermoplastic component is formed from the aforementioned thermoplastic elastomer compound. Required and optional features of these and other embodiments of the present invention are described.

As used herein, the term “Compound Tan Delta Peak Temperature” means the Tan Delta Peak Temperature for a thermoplastic elastomer compound of the present invention that comprises high softening point tackifier and styrenic block copolymer.

As used herein, the term “Copolymer Tan Delta Peak Temperature” means the Tan Delta Peak Temperature for the neat styrenic block copolymer; that is, for the styrenic block copolymer, itself, prior to combining it with any other ingredients of the thermoplastic elastomer compound of the present invention.

As used herein, the term “essentially free of” a certain component means, in some embodiments, that no amount of that component is intentionally incorporated into a compound. In other embodiments, it means that less than 1 weight percent of the component is intentionally incorporated into the compound; and, in other embodiments, it means that less than 0.1 weight percent of the component is intentionally incorporated into the compound; and, in other embodiments, it means that less than 0.01 weight percent of the component is intentionally incorporated into the compound; and, in other embodiments, it means that less than 0.001 weight percent of the component is intentionally incorporated into the compound.

As used herein, the term “high softening point tackifier” means a tackifier having a softening point of at least 80° C. according to ASTM 6493.

As used herein, the term “softening point” means a material softening temperature as measured by a ring and ball type method according to ASTM 6493.

As used herein, the term “high vinyl” means that the vinyl content of a styrenic block copolymer (prior to hydrogenation) is greater than 50 mole percent. For example, more than 50 mole percent of the polybutadiene, if present in the midblock, is polymerized at the 1,2-position, and/or, more than 50 mole percent of the polyisoprene, if present in the midblock, is polymerized at the 3,4-position, both of which by driving the polymerization with addition of a polar compound, as is well known by those of ordinary skill in the art. After hydrogenation of the high vinyl styrenic block copolymer, there is little or no vinyl unsaturation remaining. Nonetheless, such a styrenic block copolymer is still referred to as “high vinyl” because it is derived from a high vinyl precursor.

As used herein, the term “low compression set” means a compression set of less than 50%, and, in some embodiments, less than 40%, and, in other embodiments, less than 30%, at 70° C. for 22 hours according to ASTM D395.

As used herein, the term “low vinyl” means that the vinyl content of a styrenic block copolymer (prior to hydrogenation) is not greater than 50 mole percent.

As used herein, the term “room temperature” means a range of temperature of a defined environment, usually an indoor environment, which is generally considered comfortable for human habitation, and, can include, for example, any temperature ranging from about 15° C. to about 26° C.

As used herein, the term “Tan Delta” means the tangent of delta of a material and is the ratio of the material's loss modulus (E″) to the material's storage modulus (E′).

As used herein, the term “Tan Delta Peak Temperature” means the temperature at which a prominent peak appears in a graphical depiction of Tan Delta against temperature for a material, as determined by dynamic mechanical analysis using TA Instruments Dynamic Mechanical Analysis Model Q800 in “shear sandwich” mode and for a temperature scan from −40° C. to 100° C. increasing at a rate of 5° C. per minute and with an oscillation frequency of 10 Hz.

Thermoplastic Elastomer Compound

In some embodiments, the present invention is directed to a thermoplastic elastomer compound that includes styrenic block copolymer and high softening point tackifier.

It has been found that, by adding high softening point tackifier to styrenic block copolymer to provide a thermoplastic elastomer compound, the Copolymer Tan Delta Peak Temperature of the styrenic block copolymer can be shifted to a higher temperature (i.e., the Compound Tan Delta Peak Temperature). That is, for thermoplastic elastomer compounds of the present invention, the Compound Tan Delta Peak Temperature is greater than the Copolymer Tan Delta Peak Temperature.

In some embodiments, the Compound Tan Delta Peak Temperature is at least −10° C. In other embodiments, the Compound Tan Delta Peak Temperature is at least 0° C. In further embodiments, the Compound Tan Delta Peak Temperature is at least room temperature. In even further embodiments, the Compound Tan Delta Peak Temperature is from about −10° C. to about 70° C., and, in other embodiments, is from about 5° C. to about 50° C.

Styrenic Block Copolymer

Thermoplastic elastomer compounds of the present invention include one or more styrenic block copolymers.

Styrenic block copolymers that are suitable for use in the present invention include any available styrenic block copolymers that, when combined with the high softening point tackifier, can provide the thermoplastic elastomer compound with useful damping properties at the temperature of an intended end-use application, for example, room temperature or temperatures higher or lower than room temperature. Suitable styrenic block copolymers can be selected also to provide other properties desirable for the end-use application. The present invention contemplates the use of a single type of styrenic block or combinations of two or more different types of styrenic block copolymers.

Non-limiting examples of suitable styrenic block copolymers include styrene-ethylene/butylene-styrene (SEBS), styrene-ethylene/propylene-styrene (SEPS), styrene-ethylene/ethylene/propylene-styrene (SEEPS), styrene-isobutylene-styrene (SIBS), styrene-butadiene-styrene (SBS), styrene-isoprene-styrene (SIS), and combinations thereof.

In some embodiments, the styrenic block copolymer is hydrogenated, such as partially hydrogenated or fully hydrogenated.

In some embodiments, the styrenic block copolymer is selected from hydrogenated styrene-isoprene-styrene block copolymer with hydrogenated vinylic isoprene midblock or high vinyl styrene-(ethylene/butylene)-styrene block copolymer or combinations of these and/or other styrenic block copolymers.

Examples of commercially available hydrogenated styrene-isoprene-styrene block copolymer with hydrogenated vinylic isoprene midblock include one or more of the HYBRAR brand of styrenic block copolymers from Kuraray, Co. Ltd., such as grades KL-7125 and KL-7135.

HYBRAR KL-7125 copolymer is reported by the manufacturer as having a Tan Delta Peak Temperature of −5° C., a Shore A hardness of 64, a tensile elongation of 680%, and a melt flow rate (MFR) of 4 g/10 min at 230° C. with a 2.16 kg weight.

HYBRAR KL-7135 copolymer, which has a relatively higher molecular weight than that of HYBRAR KL-7125 copolymer but is similar in chemical structure, is reported by the manufacturer as having a Tan Delta Peak Temperature of +1° C., a Shore A hardness of 68, and a tensile elongation of 550%. Because of the higher molecular weight, MFR is not measurable at 230° C. and a 2.16 kg weight.

Examples of commercially available high vinyl styrene-(ethylene/butylene)-styrene block copolymer include one or more of the KRATON brand, including the KRATON ERS brand, of styrenic block copolymers from Kraton Polymers LLC, such as grades G1641, G1642, G1643, G1645, MD6958, and MD6959. KRATON brand G series styrenic block copolymers are known to have glass transition temperatures (Tg) ranging from around −55° C. to around −38° C.

As used herein, “high vinyl” means that the vinyl content of the styrenic block copolymer (prior to hydrogenation) is greater than 50 mole percent. In some embodiments, the vinyl content of the styrenic block copolymer is from about 55 to about 90 mole percent, and, in further embodiments, from about 65 to about 90 mole percent.

The high vinyl styrene-(ethylene/butylene)-styrene block copolymer has an ethylene/butylene midblock that is the hydrogenation product of 1,3-butadiene.

Suitable high vinyl styrene-(ethylene/butylene)-styrene block copolymer include those as described in, for example, U.S. Pat. No. 5,777,031 to Djiauw et al. and U.S. Pat. No. 6,984,688 to Gu, each of which is incorporated herein by reference.

It is to be understood that an isoprene midblock that is hydrogenated is converted to an ethylene/propylene midblock. Similarly, it is to be understood that a butadiene midblock that is hydrogenated is converted to an ethylene/butylene midblock.

Examples of other commercially available styrenic block copolymers include hydrogenated styrenic block copolymer available under the SIBSTAR brand from Kaneka, and hydrogenated styrenic block copolymer available under the S.O.E. brand from Asahi KASEI. Additional examples of other commercially available styrenic block copolymers include styrene-isoprene-styrene block copolymer available under the VECTOR brand from TSRC/Dexco, such as the 4000 series, and under the KRATON brand from Kraton Polymers LLC, such as the D1100 series.

In some embodiments, suitable styrenic block copolymers have a relatively high weight average molecular weight. For example, suitable styrenic block copolymers can have weight average molecular weights in excess of 75,000 and preferably in excess of 200,000. In some embodiments, the styrenic block copolymer has a weight average molecular weight ranging from about 75,000 to about 1 million or from about 75,000 to about 500,000. In other embodiments, the styrenic block copolymer has a weight average molecular weight ranging from about 200,000 to about 1 million or from about 200,000 to about 500,000.

The styrenic block copolymer has a Copolymer Tan Delta Peak Temperature. As discussed above, by adding high softening point tackifier to styrenic block copolymer to provide a thermoplastic elastomer compound, the Copolymer Tan Delta Peak Temperature of the styrenic block copolymer can be shifted to a higher temperature (i.e., the Compound Tan Delta Peak Temperature).

It is believed that the high softening point tackifier is more effective at shifting the Copolymer Tan Delta Peak Temperature to a higher temperature for styrenic block copolymers having a Copolymer Tan Delta Peak Temperature that is greater than about −40° C. but, for example, less than about −10° C., or, as a further example, less than about 0° C., or, as an even further example, less than room temperature, or, as yet a further example, less than a temperature greater than room temperature.

In some embodiments, styrenic block copolymers have a Copolymer Tan Delta Peak Temperature that is greater than about −40° C. but less than −10° C., or, less than 0° C., or, less than room temperature, or, less than a temperature greater than room temperature. In further embodiments, the thermoplastic elastomer compound is essentially free of styrenic block polymers having a Copolymer Tan Delta Peak Temperature that is less than about −40° C.

In even further embodiments, the thermoplastic elastomer compound is essentially free of styrene-(ethylene-ethylene/propylene)-styrene block copolymer or low vinyl styrene-(ethylene/butylene)-styrene block copolymer or both. Some standard or low vinyl styrenic block copolymers, such as those available under the SEPTON brand from Kuraray Co., Ltd. and including SEPTON 4000 Series SEEPS copolymers, typically have a Copolymer Tan Delta Peak Temperature that is less than about −40° C.

In other embodiments, the thermoplastic elastomer compound is essentially free of hydrogenated styrene-isoprene-styrene block copolymer with hydrogenated vinylic isoprene midblock. Some commercially available examples of such styrenic block copolymers, such as those available from Kuraray Co., Ltd., under the HYBRAR brand, including grades 7125 and 7135, can be more expensive and thus economically less desirable for some end-use applications.

High Softening Point Tackifier

Thermoplastic elastomer compounds of the present invention include one or more high softening point tackifiers.

By adding high softening point tackifier to styrenic block copolymer, the Copolymer Tan Delta Peak Temperature of the styrenic block copolymer can be shifted to a higher temperature (i.e., the Compound Tan Delta Peak Temperature).

High softening point tackifiers that are suitable for use in the present invention have a softening point of at least about 80° C. according to ASTM 6493. In some embodiments, the softening point is at least 100° C., and, in other embodiments, at least about 120° C., and, in further embodiments, at least about 140° C. In even further embodiments, the softening point ranges from about 80° C. to about 150° C.

Suitable high softening point tackifiers include those derived from rosin feedstock, terpene feedstock, or hydrocarbon feedstock. Hydrocarbon-based high softening point tackifiers can be aliphatic or aromatic, and saturated or unsaturated.

Examples of commercially available high softening point tackifiers include hydrogenated hydrocarbon resins available under the ARKON brand, such as grades P100, P115, P125, and P140, from Arakawa Chemical Industries, Ltd.; hydrogenated hydrocarbon resins available under the EASTOTAC brand, such as grades H-125-W, H-140-W, and H-142-W, from Eastman Chemical Company; hydrogenated hydrocarbon resins available under the PLASTOLYN brand, such as grade R1140, from Eastman Chemical Company; and hydrogenated hydrocarbon resins available under the REGALREZ brand, such as grade 1139, from Eastman Chemical Company.

In some embodiments, the high softening point tackifier includes an amorphous hydrocarbon resin derived from aromatic hydrocarbon feedstock. In further embodiments, the high softening point tackifier is fully hydrogenated and has a saturated cyclo-aliphatic structure.

In some embodiments, the high softening point tackifier has a weight average molecular weight ranging from about 400 to about 3,500. In other embodiments, the high softening point tackifier has a weight average molecular weight ranging from about 1,000 to about 2,000.

High softening point tackifier is included in the thermoplastic elastomer compound of the present invention in amount ranging from about 20 parts by weight to about 200 parts by weight, per 100 parts by weight of the styrenic block copolymer. In some embodiments, the amount of high softening point tackifier ranges from about 30 parts by weight to about 150 parts by weight, per 100 parts by weight of the styrenic block copolymer.

It is believed that, in general, a relatively higher proportion of high softening point tackifier is required to shift the Tan Delta Peak Temperature to a higher temperature for styrenic block copolymer having a relatively higher molecular weight. Conversely, it is believed that, in general, a relatively lower proportion of high softening point tackifier is required to shift the Tan Delta Peak Temperature to a higher temperature for styrenic block copolymer having a relatively lower molecular weight.

Care should be taken to ensure that the thermoplastic elastomer compound of the present invention is formulated to provide properties desirable for a TPE compound and not properties more commonly observed in adhesive compositions. Generally, adhesive compositions are different from TPE compounds at least because adhesive compositions typically are relatively low viscosity compositions which do not possess the useful mechanical properties of TPE compounds. Accordingly, even if up to about 200 parts by weight of high softening point tackifier is used per 100 parts by weight of styrenic block copolymer, the thermoplastic elastomer compound of the present invention is not an adhesive composition. For example, the thermoplastic elastomer compound is not tacky, or it is not sticky to the touch of a human hand.

Optional Plasticizer

In some embodiments, the thermoplastic elastomer compound further includes plasticizer. Plasticizer can be used, for example, to adjust softness and/or improve flow or other properties of the thermoplastic elastomer compound.

Any conventional oil capable of plasticizing styrenic block copolymer, such as mineral oil, vegetable oil, synthetic oil, etc., can be used in the present invention. Examples of commercially available oils include those available under the PURETOL 380 brand from Petro-Canada, and those available under the PRIMOL 382 brand from ExxonMobil.

In some embodiments, plasticizers with a higher molecular weight than that of the aforementioned conventional oils can be used. Polyisobutene (PIB) is an example of such a plasticizer with a relatively higher molecular weight. For example, medium- to high-molecular weight PIB is commercially available under the OPPANOL brand from BASF.

Optional Filler

In some embodiments, the thermoplastic elastomer compound further includes inorganic filler.

Inorganic filler can be used, for example, to lower the cost and/or control properties of the thermoplastic elastomer compound. In other embodiments, the inorganic filler also can be used, for example, as a mineral filler flame retardant.

Non-limiting examples of inorganic fillers include iron oxide, zinc oxide, magnesium oxide, titanium oxide, zirconium oxide, titanium dioxide, alumina, silica, silica-alumina, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, magnesium carbonate, calcium carbonate (heavy, light, colloidal), barium sulfate, calcium sulfate, sodium sulfate, calcium sulfite, calcium silicate, calcium phosphate, magnesium phosphate, talc, mica, kaolin, clay, wollastonite, hydrotalcite, glass beads, glass powders, silica sand, silica rock, silicon nitride, quartz powder, volcanic pumice, diatomaceous earth, white carbon, iron powder and aluminum powder.

In some embodiments, the inorganic filler is calcium carbonate, talc, or mixtures thereof.

Optional Secondary Polymer

In some embodiments, the thermoplastic elastomer compound further includes secondary polymer. Secondary polymer should be compatible with the styrenic block copolymer and can, for example, contribute to improved processability or desirable physical properties, such as hardness, in the thermoplastic elastomer compound.

Suitable secondary polymer includes polyolefin-based resins, including homopolymers, copolymers, blends of polymers, mixtures of polymers, alloys of polymers, and combinations thereof.

Non-limiting examples of polyolefins suitable for use in the present invention include polyethylene (including low-density (LDPE), high-density (HDPE), ultra-high molecular weight (UHDPE), linear-low-density (LLDPE), very-low density, etc.), maleated polypropylene, polypropylene, polybutylene, polyhexalene, polyoctene, and copolymers thereof, olefin block copolymer such as ethylene/alpha-olefin interpolymer, and ethylene-vinyl-acetate (EVA) copolymer. In some embodiments, high density polyethylene (HDPE) and/or polypropylene (PP) are preferred. Such polyolefins are commercially available from a number of sources.

Suitable secondary polymer also includes rubber, such as butyl rubber and ethylene propylene diene monomer (EPDM) rubber. The rubber can be crosslinked or non-crosslinked.

Mixtures, blends, or alloys of secondary polymer include, for example, a thermoplastic vulcanizate (TPV) that is a blend of a continuous phase of a polyolefin such as polypropylene and a discontinuous phase of a vulcanized rubber such as crosslinked EPDM.

Suitable secondary polymer also includes polyphenylene ethers (PPE). Use of PPE can help improve compression set of the thermoplastic elastomer compound. Non-limiting examples of types of PPE, sometimes also referred to as polyphenylene oxide, can include poly(2,6-dimethyl-1,4-phenylene ether), poly(2,6-diethyl-1,4-phenylene ether), poly(2-methyl-6-ethyl-1,4-phenylene ether), poly(2-methyl-6-propyl-1,4-phenylene ether), poly(2,6-dipropyl-1,4-phenylene ether), poly(2-ethyl-6-propyl-1,4-phenylene ether), poly(2,6-dimethoxy-1,4-phenylene ether), poly(2,6-di(chloro methyl)-1,4-phenylene ether), poly(2,6-di(bromo methyl)-1,4-phenylene ether), poly(2,6-diphenyl-1,4-phenylene ether), poly(2,6-ditoluyl-1,4-phenylene ether), poly(2,6-dichloro-1,4-phenylene ether), poly(2,6-dibenzyl-1,4-phenylene ether), poly(2,5-dimethyl-1,4-phenylene ether), and combinations thereof.

Optional Bonding Agent

In some embodiments in which the thermoplastic elastomer compound is overmolded onto a thermoplastic substrate, the thermoplastic elastomer compound further includes at least one bonding agent.

For embodiments in which the thermoplastic substrate is polyamide (nylon), suitable bonding agents include maleic anhydride functionalized polymers, such as maleic anhydride functionalized polyolefin and maleic anhydride functionalized styrenic block copolymer. For example, suitable maleic anhydride functionalized polyolefins are described in U.S. Pat. No. 7,842,747 to Gu et al., which is incorporated herein by reference.

Examples of commercially available maleic anhydride functionalized polyolefin include those available under the EXXELOR brand from ExxonMobil Chemical; those available under the POLYBOND brand from Addivant; and those available under the FUSABOND brand from DuPont.

Examples of commercially available maleic anhydride functionalized styrenic block copolymer include those available under the KRATON FG brand, such as grades FG1901 and FG1924, from Kraton Performance Polymers Inc.

For embodiments in which the thermoplastic substrate is a polyolefin such as polypropylene, suitable bonding agents include compatible polyolefins such as those described above as secondary polymers, including polypropylene. Commercially available examples include polypropylene available under the BRASKEM H521 brand from Braskem America Inc.

For embodiments in which the thermoplastic substrate is a another thermoplastic material such as thermoplastic polyurethane (TPU), polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), and polybutylene terephthalate/polycarbonate (PBT/PC), suitable bonding agents include compatible polymers such as TPU or copolyester elastomer (COPE) or blends of TPU/COPE. Commercially available examples include TPU available under the ELASTOLLAN brand from BASF.

Other Optional Additives

In some embodiments, the thermoplastic elastomer compound further includes conventional plastics additives in an amount that is sufficient to obtain a desired processing or performance property for the compound. The amount should not be wasteful of the additive nor detrimental to the processing or performance of the compound. Those skilled in the art of thermoplastics compounding, without undue experimentation but with reference to such treatises as Plastics Additives Database (2004) from Plastics Design Library (elsevier.com), can select from many different types of additives for inclusion into the compounds of the present invention.

Non-limiting examples of optional additives that can be included in the thermoplastic elastomer compounds of the present invention include adhesion promoters; biocides; anti-fogging agents; anti-static agents; blowing and foaming agents; bonding agents and bonding polymers; curing agents or systems; dispersants; flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of any of the aforementioned additives.

In some embodiments, the thermoplastic elastomer compound further includes a physical foaming agent, such as carbon dioxide, nitrogen, or air, and/or a chemical foaming agent, such as organic or inorganic compounds that release gases upon decomposition, and can be injection molded or extruded into a foamed TPE material.

In other embodiments, the thermoplastic elastomer compound further includes a curing system such as a peroxide curing system. Use of such a curing system can help improve compression set.

Ranges of Ingredients in the TPE Compounds

Table 1 below shows the acceptable, desirable, and preferable ranges of ingredients for the thermoplastic elastomer compound of the present invention, based on 100 parts by weight of the styrenic block copolymer included in the thermoplastic elastomer compound.

The thermoplastic elastomer compound of the present invention can comprise, consist essentially of, or consist of these ingredients. Any number between the ends of the ranges is also contemplated as an end of a range, such that all possible combinations are contemplated within the possibilities of Table 1 as embodiments of compounds for use in the present invention. Unless expressly stated otherwise herein, any disclosed number is intended to refer to exactly the disclosed number, “about” the disclosed number, or both exactly the disclosed number and “about” the disclosed number.

TABLE 1 Thermoplastic Elastomer Compound (parts by weight per 100 parts by weight of SBC) Ingredient Acceptable Desirable Preferable Styrenic Block Copolymer 100 100 100 High Softening Point Tackifier 20 to 200  30 to 170 35 to 140 Optional Plasticizer 0 to 200 20 to 150 40 to 100 Optional Filler 0 to 150  0 to 100 0 to 80 Optional Secondary Polymer 0 to 300  0 to 200  0 to 150 Optional Bonding Agent 0 to 300  0 to 200  0 to 150 Optional Other Additives 0 to 100 0 to 80 0 to 50

In some embodiments, the thermoplastic elastomer compound can include at least about 50 parts, or, at least about 70 parts, but less than about 100 parts, or less than about 80 parts, by weight of high softening point tackifier, based on 100 parts by weight of the styrenic block copolymer included in the thermoplastic elastomer compound. In further embodiments, it is possible to achieve desirable low compression set and useful damping properties from thermoplastic elastomer compounds of the present invention that include less than about 40 weight percent, or, in some embodiments, less than about 35 weight percent, or, in other embodiments, less than about 25 weight percent, or, in further embodiments, less than about 20 weight percent, of styrenic block copolymer.

In other embodiments, the thermoplastic elastomer compound includes less than 30 weight percent of high softening point tackifier based on total weight of the compound. In even further embodiments, the thermoplastic elastomer compound includes less than 28 weight percent of high softening point tackifier based on total weight of the compound.

Processing

The preparation of thermoplastic elastomer compounds of the present invention is uncomplicated once the proper ingredients have been selected. The compound of the present can be made in batch or continuous operations.

Mixing in a continuous process typically occurs in an extruder that is elevated to a temperature that is sufficient to melt the polymer matrix with addition of all additives at the feed-throat, or by injection or side-feeders downstream. Extruder speeds can range from about 200 to about 700 revolutions per minute (rpm), and preferably from about 300 rpm to about 500 rpm. Typically, the output from the extruder is pelletized for later extrusion, molding, thermoforming, foaming, calendering, and/or other processing into polymeric articles.

Subsequent extrusion, molding, thermoforming, foaming, calendering, and/or other processing techniques are well known to those skilled in the art of thermoplastics polymer engineering. Without undue experimentation but with such references as “Extrusion, The Definitive Processing Guide and Handbook”; “Handbook of Molded Part Shrinkage and Warpage”; “Specialized Molding Techniques”; “Rotational Molding Technology”; and “Handbook of Mold, Tool and Die Repair Welding”, all published by Plastics Design Library (www.elsevier.com), one can make articles of any conceivable shape and appearance using compounds of the present invention.

Article Formed from the TPE Compound

In some embodiments, the present invention is directed to an article formed from the thermoplastic elastomer compound as described herein. In addition to exhibiting useful damping properties at or above room temperature, the article has low compression set properties.

The article has low compression set meaning that it has a compression set of, in some embodiments, less than about 50%, and, in other embodiments, less than 40%, and, in further embodiments, less than 30%. In each case, compression set is determined at 70° C. for 22 hours according to ASTM D395.

It is possible to achieve desirable low compression set and useful damping properties in articles formed from thermoplastic elastomer compounds of the present invention that include less than about 40 weight percent, or, in some embodiments, less than about 35 weight percent, or, in other embodiments, less than about 25 weight percent, or, in further embodiments, less than about 20 weight percent, of styrenic block copolymer.

In some embodiments, the article is shaped in the form of a seal, piping, gasket, washer, O-ring, or the like. In such embodiments, the article can be any of any suitable cross-sectional shape, for example, substantially circular, annular, elliptical, ring-shaped, disk-shaped, or polygonal (e.g., with from about 3 to about 10 sides). In some of such embodiments, the article has a substantially uniform thickness. In other of such embodiments, the article has a varying thickness.

In other embodiments, the present invention is directed to a multi-component article which includes at least two components formed from different materials one of which is the thermoplastic elastomer compound as described herein. For example, the thermoplastic elastomer compound can be overmolded onto a substrate. In some embodiments, the substrate is a thermoplastic substrate such as polyamide (nylon) or polyolefin (e.g., polypropylene) or another thermoplastic material such as thermoplastic polyurethane (TPU), polycarbonate (PC), polycarbonate/acrylonitrile butadiene styrene (PC/ABS), or polybutylene terephthalate/polycarbonate (PBT/PC). According to the present invention, the thermoplastic elastomer compound overmolded onto a thermoplastic substrate has 90 degree peel strength of, in some embodiments, greater than about 8 pounds per inch, and, in other embodiments, greater than about 10 pounds per inch.

In further embodiments, the article or a component of the multi-component article can be formed from the TPE compound by injection molding, extruding, thermoforming, calendering, blow molding, and via additive 3-D manufacturing.

The article of the present invention can comprise, consist essentially of, or consist of, the thermoplastic elastomer compound.

Usefulness of the Invention

As discussed above, thermoplastic elastomer compounds of the present invention and articles formed therefrom exhibit useful damping properties (e.g., vibration and/or sound damping) at or above room temperature while also exhibiting low compression set properties.

It has been found that, by adding high softening point tackifier to styrenic block copolymer to provide a thermoplastic elastomer compound, the Copolymer Tan Delta Peak Temperature of the styrenic block copolymer can be shifted to a higher temperature (i.e., the Compound Tan Delta Peak Temperature). Advantageously, the damping capacity of the styrenic block copolymer can be increased for an intended end-use application at a given temperature, for example, at least −10° C., or at least 0° C., or at room temperature, or greater than room temperature. Such an improvement in damping capacity can be achieved even for certain high molecular weight styrenic block copolymer. Because high molecular weight styrenic block copolymer can be used, low compression set properties also can be achieved.

Accordingly, thermoplastic elastomer compounds of the present invention can be used to form any article or any component of a multi-component article which requires a combination of low compression set and useful damping capacity for applications at temperatures that are, for example, at least −10° C., or at least 0° C., or at room temperature, or greater than room temperature.

Because of its usefulness and versatility and relative economic favorability, the thermoplastic elastomer compound of the present invention has potential for a variety of applications in many different industries, including but not limited to: automotive and transportation; household appliances; industrial equipment; electronics; acoustics; communications; healthcare and medical; defense; firearms; security; personal safety; and other industries or applications benefiting from a combination of low compression set and vibration and/or sound damping or isolation.

The combination of useful damping properties at or above room temperature and low compression set properties makes the article of the present invention especially useful as a seal or a piping or a gasket or a washer or an 0-ring, or the like.

EXAMPLES

Non-limiting examples of thermoplastic elastomer compounds of various embodiments of the present invention are provided.

Examples Showing Effect of High Softening Point Tackifier

Table 2a below shows sources of ingredients for the thermoplastic elastomer compounds of Examples 1 to 8 and Comparative Example A.

TABLE 2a Chemical Brand Source Hydrogenated styrene-isoprene- HYBRAR Kuraray styrene block copolymer with 7135 hydrogenated vinylic isoprene midblock High vinyl styrene- KRATON Kraton (ethylene/butylene)-styrene block MD6958 copolymer (Very high molecular weight) White mineral oil 380 vis USP (numerous) white oil Hydrocarbon resin PLASTOLYN Eastman R1140 Chemical Polyethylene resin DOWLEX 2035 Dow Chemical Calcium carbonate (limestone) VICRON 25-11 Specialty Minerals Wax KEMAMIDE E PMC Biogenix Antioxidant IRGANOX 1010 BASF

Table 2b below shows the formulations and certain properties of Examples 1 to 4 and Comparative Example A.

TABLE 2b Example A 1 2 Ingredient Parts Wt. % Parts Wt. % Parts Wt. % HYBRAR 7135 100 38.26 100 35.54 100 33.18 380 vis USP white oil 80 30.60 80 28.43 80 26.54 PLASTOLYN R1140 0 0 20 7.11 40 13.27 DOWLEX 2035 40 15.30 40 14.21 40 13.27 VICRON 25-11 40 15.30 40 14.21 40 13.27 KEMAMIDE E 0.7 0.27 0.7 0.25 0.7 0.23 IRGANOX 1010 0.7 0.27 0.7 0.25 0.7 0.23 TOTAL 261.4 100.00 281.4 100.00 321.4 100.00 Tan Delta Peak Height (unitless) 0.20 0.27 0.45 Compound Tan Delta (Not (Not 5 Peak Temperature (deg C.) available) available) Example 3 4 Ingredient Parts Wt. % Parts Wt. % HYBRAR 7135 100 31.11 100 29.29 380 vis USP white oil 80 24.89 80 23.43 PLASTOLYN R1140 60 18.67 80 23.43 DOWLEX 2035 40 12.45 40 11.72 VICRON 25-11 40 12.45 40 11.72 KEMAMIDE E 0.7 0.22 0.7 0.21 IRGANOX 1010 0.7 0.22 0.7 0.21 TOTAL 321.4 100.00 321.4 100.00 Tan Delta Peak Height 0.75 0.95 (unitless) Compound Tan Delta 10 20 Peak Temperature (deg C.)

Table 2c below shows the formulations and certain properties of Examples 5 to 8.

TABLE 2c Example 5 6 7 8 Ingredient Parts Wt. % Parts Wt. % Parts Wt. % Parts Wt. % KRATON 100 33.18 100 31.11 100 29.29 100 27.67 MD6958 380 vis USP 80 26.54 80 24.89 80 23.43 80 22.14 white oil PLASTOLYN 40 13.27 60 18.67 80 23.43 100 27.67 R1140 DOWLEX 40 13.27 40 12.45 40 11.72 40 11.07 2035 VICRON 25-11 40 13.27 40 12.45 40 11.72 40 11.07 KEMAMIDE E 0.7 0.23 0.7 0.22 0.7 0.21 0.7 0.19 IRGANOX 0.7 0.23 0.7 0.22 0.7 0.21 0.7 0.19 1010 TOTAL 301.4 100.00 321.4 100.00 341.4 100.00 361.4 100.00 Tan Delta Peak Height (unitless) 0.65 0.70 0.85 0.85 Compound Tan 3 2 7 16 Delta Peak Temperature (deg C.)

Examples of TPE Compounds with Low Compression Set

Table 3a below shows sources of ingredients for the thermoplastic elastomer compounds of Examples 9 to 14, which can be useful for end-use applications requiring low compression set and good damping capacity (e.g., vibration and/or sound damping).

TABLE 3a Chemical Brand Source Styrene-(ethylene/ethylene/propylene)- SEPTON Kuraray styrene block copolymer 4077 Hydrogenated styrene-isoprene-styrene HYBRAR Kuraray block copolymer with hydrogenated 7135 vinylic isoprene midblock High vinyl styrene-(ethylene/butylene)- KRATON Kraton styrene block copolymer (Very high MD6958 molecular weight) White mineral oil PAROL 500 Petro-Canada Polyphenylene ether LXR 040C Bluestar New Chemical Materials Hydrocarbon resin PLASTOLYN Eastman R1140 Chemical HDPE SCLAIR NOVA 2908 Chemicals Wax KEMAMIDE PMC E Biogenix Antioxidant IRGANOX BASF 1010

Table 3b below shows the formulations and certain properties of Examples 9 to 14.

TABLE 3b Example 9 10 11 Ingredient Parts Wt. % Parts Wt. % Parts Wt. % SEPTON 4077 50 16.07 50 14.88 50 13.85 HYBRAR 7135 50 16.07 50 14.88 50 13.85 KRATON MD6958 0 0 0 0 0 0 PAROL 500 80 25.71 80 23.80 80 22.15 LXR 040C 30 9.64 30 8.93 30 8.31 PLASTOLYN R1140 75 34.11 75 22.31 75 20.77 SCLAIR 2908 25 8.04 50 14.88 75 20.77 KEMAMIDE E 0.42 0.13 0.42 0.12 0.42 0.12 IRGANOX 1010 0.7 0.22 0.7 0.21 0.7 0.19 TOTAL 311.1 100.00 336.1 100.00 361.1 100.00 Hardness (Shore A) 41 57 69 Tensile (psic) 670 910 1130 Elongation (%) 580 590 720 Compression set (%) 15 18 24 (70 deg C., 22 h) (ASTM D395) Example 12 13 14 Ingredient Parts Wt. % Parts Wt. % Parts Wt. % SEPTON 4077 50 16.33 0 0 0 0 HYBRAR 7135 50 16.33 0 0 0 0 KRATON MD6958 0 0 100 32.13 100 29.74 PAROL 500 80 26.13 80 25.71 80 23.80 LXR 040C 0 0 30 9.64 30 8.92 PLASTOLYN R1140 75 24.50 75 24.10 75 22.31 SCLAIR 2908 50 16.33 25 8.03 50 14.87 KEMAMIDE E 0.42 0.14 0.5 0.16 0.5 0.15 IRGANOX 1010 0.7 0.23 0.7 0.22 0.7 0.21 TOTAL 306.1 100.00 311.2 100.00 336.2 100.00 Hardness (Shore A) 48 28 48 Tensile (psic) 720 500 610 Elongation (%) 640 560 590 Compression set (%) 23 21 28 (70 deg C., 22 h) (ASTM D395)

Without undue experimentation, those having ordinary skill in the art can utilize the written description of the present invention, including the Examples, to formulate thermoplastic elastomer compounds and make articles therefrom which exhibit useful damping properties at or above room temperature while also exhibiting useful low compression set properties.

All documents cited in the Embodiments of the Invention are, in relevant part, incorporated herein by reference; the citation of any document is not to be construed as an admission that it is prior art with respect to the present invention.

While particular embodiments of the present invention have been illustrated and described, it would be obvious to those skilled in the art that various other changes and modifications can be made without departing from the spirit and scope of the invention. It is therefore intended to cover in the appended claims all such changes and modifications that are within the scope of the present invention. 

What is claimed is:
 1. An article formed from a thermoplastic elastomer compound, the compound comprising: (a) styrenic block copolymer having a Copolymer Tan Delta Peak Temperature; and (b) tackifier having a softening point of at least about 80° C. according to ASTM 6493; wherein the compound has a Compound Tan Delta Peak Temperature, and the Compound Tan Delta Peak Temperature is greater than the Copolymer Tan Delta Peak Temperature; and wherein the article has a compression set of less than about 50% at 70° C. for 22 hours according to ASTM D395.
 2. The article of claim 1, wherein the compound is essentially free of styrene-(ethylene-ethylene/propylene)-styrene block copolymer and low vinyl styrene-(ethylene/butylene)-styrene block copolymer.
 3. The article of claim 1, wherein the styrenic block copolymer is high vinyl styrene-(ethylene/butylene)-styrene block copolymer.
 4. The article of claim 1, wherein the Copolymer Tan Delta Peak Temperature is greater than −40° C. but less than −10° C.
 5. The article of claim 1, wherein the Compound Tan Delta Peak Temperature is at least −10° C.
 6. The article of claim 1, wherein the tackifier has a softening point ranging from about 80° C. to about 150° C. according to ASTM
 6493. 7. The article of claim 1, wherein the tackifier has a weight average molecular weight ranging from about 400 to about 3,500.
 8. The article of claim 1, wherein the tackifier comprises a saturated cyclo-aliphatic amorphous hydrocarbon resin.
 9. The article of claim 1, wherein the tackifier is present in an amount ranging from about 20 parts by weight to about 200 parts by weight, per 100 parts by weight of the styrenic block copolymer.
 10. The article of claim 1, wherein the compound further comprises secondary polymer.
 11. The article of claim 1, wherein the compound further comprises at least one additive selected from the group consisting of adhesion promoters; biocides; anti-fogging agents; anti-static agents; blowing and foaming agents; bonding agents and bonding polymers; curing agents or systems; dispersants; filler; flame retardants and smoke suppressants; impact modifiers; initiators; lubricants; micas; pigments, colorants and dyes; plasticizer; processing aids; release agents; silanes, titanates and zirconates; slip and anti-blocking agents; stabilizers; stearates; ultraviolet light absorbers; viscosity regulators; waxes; and combinations of any of the aforementioned additives.
 12. The article of claim 1, wherein the compound comprises less than about 40 weight percent of the styrenic block copolymer based on total weight of the compound.
 13. The article of claim 1, wherein the article has a compression set of less than about 30% at 70° C. for 22 hours according to ASTM D395.
 14. The article of claim 1, wherein the article is a seal or a gasket.
 15. A multi-component plastic article comprising at least two components formed from different thermoplastic materials, wherein at least one of the at least two components is the article of claim 1 and at least one other of the at least two components is a thermoplastic substrate onto which the article of claim 1 is overmolded. 